The present invention relates to a swash plate type variable displacement compressor.
Japanese Laid-Open Patent Publications No. 2-19665 and No. 5-172052 disclose conventional swash plate type variable displacement type compressors (hereinafter, referred to as compressors). The compressors include a suction chamber, a discharge chamber, a swash plate chamber, and a plurality of cylinder bores, which are formed in a housing. A drive shaft is rotationally supported in the housing. The swash plate chamber accommodates a swash plate, which is rotatable through rotation of the drive shaft. A link mechanism, which allows change of the inclination angle of the swash plate, is arranged between the drive shaft and the swash plate. The inclination angle is defined with respect to a line perpendicular to the rotation axis of the drive shaft.
Each of the cylinder bores accommodates a piston in a reciprocal manner and thus forms a compression chamber. Each cylinder bore is formed by a front cylinder bore arranged in front of the swash plate and a rear cylinder bore arranged behind the swash plate. Each piston includes front head, which reciprocates in the front cylinder bore, and a rear head, which is integral with the front head and reciprocates in the rear cylinder bore.
A conversion mechanism reciprocates each of the pistons in the associated one of the cylinder bores by the stroke corresponding to the inclination angle of the swash plate through rotation of the swash plate. An actuator is capable of changing the inclination angle of the swash plate and controlled by a control mechanism.
In the compressor described in Japanese Laid-Open Patent Publication No. 2-19665, a pressure regulation chamber is formed in a rear housing member of the housing. A control pressure chamber is formed in a cylinder block, which is also a component of the housing, and communicates with the pressure regulation chamber. The actuator is arranged in the control pressure chamber, while being prevented from rotating integrally with the drive shaft.
Specifically, the actuator has a non-rotational movable body that overlaps with a rear end portion of the drive shaft. The inner peripheral surface of the non-rotational movable body rotationally supports the rear end portion of the drive shaft. The non-rotational movable body is movable in the direction of the rotation axis of the drive shaft. The non-rotational movable body is slidable in the control pressure chamber through the outer peripheral surface of the non-rotational movable body and slides in the direction of the rotation axis of the drive shaft. The non-rotational movable body is restricted from sliding about the rotation axis of the drive shaft. A pressing spring, which urges the non-rotational movable body forward, is arranged in the control pressure chamber or the pressure regulation chamber. The actuator has a movable body, which is joined to the swash plate and movable in the direction of the rotation axis of the drive shaft. A thrust bearing is arranged between the non-rotational movable body and the movable body. A pressure control valve, which changes the pressure in the control pressure chamber, is provided between the pressure regulation chamber and the discharge chamber. Through such change of the pressure in the control pressure chamber, the non-rotational movable body and the movable body are moved along the rotation axis.
The link mechanism is arranged in the swash plate chamber. The link mechanism has a movable body and a lug arm fixed to the drive shaft. A rear end portion of the lug arm has an elongated hole. The elongated hole extends in a direction that is perpendicular to the rotation axis of the drive shaft and transverse to rotation axis of the drive shaft. A pin is received in the elongated hole and supports the swash plate at a position forward to the swash plate such that the swash plate is allowed to pivot about a first pivot axis.
In the compressor described in Japanese Laid-Open Patent Publication No. 5-172052, a front end portion of the movable body also has an elongated hole, which extends in the direction perpendicular to and transverse to the rotation axis of the drive shaft. A pin is passed through the elongated hole and supports the swash plate at the rear end of the swash plate such that the swash plate is allowed to pivot about a second pivot axis, which is parallel to the first pivot axis.
In these compressors, when a pressure regulation valve is controlled to open, communication between the discharge chamber and the pressure regulation chamber is allowed, which raises the pressure in the control pressure chamber compared to the pressure in the swash plate chamber. This causes the non-rotational movable body and the movable body to proceed. The inclination angle of the swash plate is thus increased and the stroke of each piston is increased correspondingly. This increases the displacement of the compressor per rotation cycle. In contrast, by controlling the pressure regulation valve to close, the communication between the discharge chamber and the pressure regulation chamber is blocked. This lowers the pressure in the control pressure chamber to a level equal to the pressure level in the swash plate chamber. This causes the non-rotational movable body and the movable body to retreat. The inclination angle of the swash plate is thus decreased and the piston stroke is decreased correspondingly in this compressor. This reduces the displacement of the compressor per rotation cycle.
In these compressors, the link mechanism is arranged such that, as the inclination angle of the swash plate is changed, the top dead center position of the piston front head is moved by a greater extent than the top dead center position of the piston rear head. Specifically, when the inclination angle of the swash plate is changed, the top dead center position of the piston rear head is scarcely moved, while the top dead center position of the piston front head is largely moved. As the inclination angle of the swash plate approaches zero degrees, the piston performs a little compression work only with the rear head, while performing no compression work with the front head.
In the above describe conventional compressors, however, the actuator is located behind the swash plate, or closer to the rear cylinder bores with respect to the swash plate. Therefore, in the housing of the compressor, it is difficult to create a space behind the swash plate for allowing the non-rotational movable body and the movable body to proceed and retreat. The size of the actuator in the radial direction thus needs to be reduced. However, it is difficult for a small actuator to perform the displacement control. If the radial size of the housing is increased to allow the inclination angle of the swash plate to be easily changed, the mountability of the compressor on a vehicle will be degraded.